This invention relates to lift gates of the type which can be mounted to a truck so as to raise and lower loads to and from the truck bed. The type of lift gate with which this invention is principally concerned has vertical rails at each side, which guide and support vertically slidable runners, to which a platform is pivotally mounted. The platform can be pivoted between a horizontal load-carrying position and an upright stored position. As a unit it is raised by pulling up the runners with a flexible member such as a chain or cable attached to each runner, and lowered by slacking off the flexible members.
This is a sound and useful construction which performs well. When the runners are pulled up, their elevations along the rails are accurately related to each other, because both chains are equally pulled, and are in tension. However, when the runners are lowered, there is no direct means coordinating them. Instead, the combined weight of the platform and the runners is relied on to keep both flexible members taut, which if it occurs will result in the platform's lowering properly. This does in fact occur under most circumstances, and definitely when the platform is loaded. However, it may occur when the platform is lowered unloaded or very lightly loaded that the grease which lubricates the rails is dirty, or congealed on a cold day, and there could be sufficient difference in resistance to sliding that one of the runners could lag behind the other. Then there could be some undesirable sideward tilt. It is an object of this invention to provide simple means to assist in keeping the platform level even if one of the runners tends to lag behind the other.